Many medical procedures involve the insertion of catheters through bodily lumens such as blood vessels, nasal passages, urethral passages and the like to reach cavities or regions of the body where a therapeutic function is to be performed. Often, the lumens are convoluted or branched, particularly in the case of blood vessels, and insertion of the catheter so that its distal end reaches the desired location involves steering and maneuvering of the catheter through delicate, narrow passages, and the bending and curving of the catheter to conform to the shapes of the passages. This quality of the catheter is commonly referred to as "steerability." Many of the sites sought to be reached are also a considerable distance from the point of entry of the catheter into the body. Pushing the catheter shaft in far enough to reach these sites requires that the shaft be stiff enough so that it will not bend back over itself or form kinks. The term "pushability" has been used to characterize this quality. To accommodate these two needs, catheters have been constructed in different ways to achieve a proximal end which is stiffer than the distal end, and many of these constructions are complicated and expensive to manufacture.
Multilumen catheters offer even greater problems since they are of larger diameter than single-lumen catheters and require open space for the lumens. The open space reduces the amount of cross-sectional area and hence the opportunity for the incorporation of structural features to add to or vary the stiffness of the catheter shaft.